1. Field of the Invention
This invention relates to the field of aircraft engine performance monitoring systems and more particularly to the field of portable or on-board test circuits used to measure the performance of the dual ignition systems. Such systems include the dual magneto powered ignition systems customarily used on reciprocating internal combustion engines such as the engines used to power light aircraft, hydroplane boats and power carts and other vehicles requiring the use of high engine power to weight ratio.
2. Description of the Prior Art
There are no known Ignition Performance Measuring Circuits for use as on-board monitoring circuits for light aircraft. Engines using a dual ignition system typically obtain maximum performance when each of the separate ignition systems are timed to provide simultaneous ignition signals in correct synchronization with the engine timing cycle. Pilots operating aircraft equipped with dual magneto ignition systems are instructed to test these systems prior to taking off by bringing the engine RPM to a predetermined level, and individually switching each magneto off while monitoring the engine RPM for an expected and limited drop of typically less than five percent. Aircraft ignition systems are not tested in flight.
There is no presently known equipment available for use on light aircraft in flight for continuously monitoring for the loss of one half of a dual magneto powered ignition system not for monitoring for a defective ignition signal to a particular spark plug since the remaining operational spark plug in the cylinder will fire the cylinder thereby preventing a cylinder miss that the pilot or operator could hear. The present procedure for checkout prior to flight allows a pilot to detect a miss firing spark plug only as the alternate ignition system is switched off by observing that one cylinder is missing from the firing order. An accompanying loss of engine RPM will also be observed. However; once both ignition systems are activated, as in flight, the pilot is again without means for detecting the loss of a firing signal in a cylinder in which the alternate ignition system is functioning since the power loss would be minimal.
Degradation of the ignition system is more likely to go un-noticed where different pilots use the aircraft such as is customary with club-owned aircraft or where the aircraft is subject to infrequent use. An un-noticed loss or partial loss of an ignition system can result in a hazardous condition for both pilot and passengers.
Ignition systems used on aircraft are typically shielded making electrical contact with the individual firing circuits impractical. Aircraft magnetos are typically sealed making contact at the magneto impractical. Establishing a timing reference is also impossible without mechanically invading the magneto housing, the shielded or armored individual ignition leads, the engine shaft gearing or by resorting to external sensors for monitoring the location of the moving propeller. The expense of incorporating an ignition performance monitoring circuit using conventional means for coupling signals from the ignition system to the test circuit is substantial and typically operates to discourage consideration of solutions to the performance monitoring problem.